Sheet Metal Work

Where a number of uniform pieces have to be made from sheet metal, but the cost of press tools is not justified for the quantity, a large copy of the outline may be made quickly in celluloid (as described on page 14), and the pieces "engraved" out of the sheet accurately and cheaply. (An example of this work is shown in Fig.24 above.)

Engraving, Drilling, Slotting and Milling at one setting

It sometimes happens that a number of small scale plates or similar parts, somewhat as shown in Fig.25, are required in thin metal, celluloid or the like, and that the quantity is too large for them to be made by hand but does not warrant the making of press tools.

Fig.25.

Such parts may be made accurately and economically on

the engraving machine with home made set copy.

In the example shown, the inscription and scales would be engraved, the holes drilled or centred, the slot cut and the plate milled out of the strip with any degree of beveling or curvature of edge desired, all at one setting.

Two or more tongues of metal would be left to connect the plate with the strip during the cutting-out operation. Fig.26, shows another example of this class of work.

Fig.26

Slotting and Milling

Small slots, either straight or in curves or circular arcs, can easily be cut on the Engraving Machine. The copy for a circular arc may be a mere link, pivoted about a point fixed on the copyholder, the radius of the link being varied by placing the style in any series of holes in the link, or by means of an adjustable slider.

Spiral Slots

Fig.27 shows a spiral slot machined in the Engraving Machine as a manufacturing operation. The slot contains half a steel ball, the other half of which lies in a radial slot in a fixed plate on which the other revolves, this combination of slots and ball forming a stop motion to limit the number of turns of the movable part to some prescribed value.

Fig.27

Involute and Cycloidal Curves

May be cut on the Engraving Machine by arranging on the copyholder appropriate wrapping or rolling connections which guide the pantograph style in the prescribed path. The machine is used for this purpose in making master cutters for gear teeth.

Locating Holes

Where a small number of holes have to be accurately located in small pieces - whether of sheet metal or otherwise - and the cost of a drilling jig is not justified by the quantity, and also where more accurate work is needed than that generally obtained from a drilling jig, an enlarged copy, consisting of a plate of metal with the holes laid out and centre punched, can be put on the copyholder, and the cutter in the form of a drill, used to drill the holes which may be finished in a drilling machine if necessary.

Cutting Cams

Fig.28.

Small cams of irregular forms which cannot be generated on any ordinary machine tool, can be cut on the Engraving Machine from enlarged copy. Fig.28 shows double internal cams produced in this way.

Fig.29.

Flat Spiral Springs

Form very convenient means of guiding and effecting small displacements, and can be readily produced on the Engraving Machine. A suitable spiral is drawn out, say, ten times full size, and using this as a guide, a celluloid copy is made as described on page 14. By this means it is as easy to work to the best theoretical outlines as to any other, and of course, the method is not restricted to the cutting out of springs.

Knurls

The Engraving Machine can be used successfully to produce knurling in sunk panels, for finger grips and the like, using a 90 degree cutter with a crisscross copy, the depth of cut being such that the sides of the cuts blend together to give a sharp diamond knurl effect.

Press Tools

Punches and dies may have their cutting edges accurately outlined from suitable enlarged models in celluloid or metal. Examples of this are shown in Fig.30. The punches A and B were profiled from relief copy. The dies C and D were cut from sunk copy.

It is difficult to secure clean blanks when punching very thin metal with ordinary press tools, because, when the thickness of the metal is of the same order as the clearance between the punch and the die, the edges of the blank are drawn out and tear raggedly, instead of shearing cleanly.

Instead of a die of the conventional type, a plain pad of rubber may be employed. The punch "immerses" the sheet metal in the rubber, which flows closely around the sharp edges of the punch, and tears the blank out cleanly.

To get the best results, the punch may

be made by engraving the outline of the blank on a suitable block of steel. The working depth of the punch is not very great ; it is sufficient to cut the groove about 1/32 inch to 1/16 inch deep. Its cross section should be as indicated in Fig.31, the blank being defined by the square edge.

Fig.31

The writing point, which is easily replaced, is made from a special heat resistance material which far outlasts the usual copper point.

The holder is of special ventilated and insulated construction. The Etcher is designed to be used either by hand, as shown in Fig.32, or in an Engraving Machine, as shown in Fig.33. In the machine the holder takes the place of the cutter and spindle, using standard copies, as illustrated on page 9.

We can supply the holder and writing point without the transformer and other accessories. This enables a customer already owning an electrical etching apparatus to enjoy the advantages possessed by our design of writing holder, and the convenience of using it in his Taylor-Hobson Engraving Machine.

Instructions for connecting up and using the Electric Resistance Etcher

Connect two wires of the main cable from the transformer to the electricity mains by means of a lamp holder adapter or a wall plug. Use the red and black wires. The third wire in this cable is the earth wire. It is coloured grey and clearly labeled. In order to comply with the Board of Trade regulations this should be coupled to the conduit casing, a water pipe or other convenient earth point.

The writing holder is connected to the red terminal in front of the transformer.

The separate flex is provided to connect the work to the other transformer terminal.

Fig.32

Ventilated and insulated writing unit which can be fitted in place of cutter spindle on any Taylor-Hobson Engraving Machine, to give perfectly controlled lettering.

Around the switch on the top of the transformer are the words "off," "minimum" and "maximum." These indicate different degrees of current to suit all conditions.

Before commencing to etch, the transformer is switched on and the marking point brought into contact with the work. Lifting the point away from the work again breaks the current.

When used in the Taylor-Hobson Engraving Machine the holder takes the place of the cutter spindle, as shown in Fig.33. It should not, however, be

clamped in position, but should remain free to be raised or lowered by hand. The copy is traced round in the usual way, the writing point being kept tightly in contact with the work by control of the hand.

Do not use the machine feed or there is a risk of breaking the marking point. This is rather brittle and should be handled with care. It should project out of its holder about 5/16 inch to 3/8 inch. If used with too short a projection the holder will get unnecessarily warm ; If it projects too far there is a risk of breaking the point.

The Taylor-Hobson "Javelin" process of electric etching (see Fig.34), is applicable to most metal surfaces, hard or soft, providing the finish is smooth and preferably ground or polished, and offers a rapid, safe and economical means of marking products with lettering, designs, trade marks, etc. The etching is effected by means of a series of minute electrical arcs, formed at the point of a rapidly vibrating electrode, linked from the master copy by pantograph reduction.

appreciably affected. The trouble and danger associated with acid etching are entirely eliminated. The "Javelin" process is clean and perfectly safe and will produce first-class work at less cost.

Supplied Singly for use on Taylor-Hobson Engraving Machine

Fig.35.

Supplied singly, see Fig.35, the "Javelin" etching units are for use with Taylor-Hobson Engraving Machines, Models "C" "CB", "CX" and "CXL" or will fit other similar engraving machines. The spindle on the unit is fitted in place of the usual rotary cutter spindle, and the machine, normally used for engraving, becomes an electric etcher.

The Single "Javelin" Etching Unit is supplied complete in case, containing adjusting key, feeler blade for cleaning magnetic face, sample "Javelins," etc. A transformer is supplied having six tapings to vary the etching current, ON-OFF switch and plugs for connecting to mains and to the unit.

Fuller information upon request.

Example :- Reduction required 1:6.5. Set the index edge of slider on the long bar 2.87 inches from the line marked 3 on the short bar 0.64 inches from the line 3 in its bar.

page 26

Example:- Reduction required 1:4.1. Set the index edge of slider on the long bar 4.09 inches from the line marked 2 on the bar and the slider on the short bar 1.02 inches from the line 2 on its bar.

page 27